This application claims the priority benefit of Taiwan application serial no. 90111230, filed May 11, 2001.
1. Field of the Invention
The present invention relates in general to a cleaning method for a semiconductor, and in particular, a cleaning method for a semiconductor manufacturing process to prevent metal corrosion by employing cathodic protection.
2. Description of the Related Art
In manufacturing technology of Very Large Scale Integration (VLSI), the most frequent step is wafer cleaning. 30% of all the manufacturing steps are dedicated to wafer cleaning, and therefore, the cleaning process of a wafer is important. The prime object of cleaning silicon wafer is to remove metal impurities and organic compound contaminants on the surface of the silicon wafer and to reduce adsorption of micro-particles. Excessive metal impurities will cause a current leakage at p-n joining surface, decrease life cycle for a minor carrier and lower breakdown voltage of an AND gate oxidation layer. In another aspect, the adsorption of the micro-particles will affect precision of image transfer in a micro-imaging process, and may further cause a short circuit in circuit structure.
The process of wafer cleaning is divided into two stages. The first stage is known as a front end of line (FEOL) cleaning, for instance, a pre-cleaning of the dispersion and epitaxial fabrication process, removal of an oxide layer and a silicon oxide layer and etching and removal of a polycrystalline silicon. The next stage is the back end of line (BEOL) cleaning, for instance, cleaning of dielectric layer between metals, cleaning following etching of a metal layer, cleaning before and after the removal of photo-resist, cleaning after CMP and reclamation of a wafer.
There are three important objectives in the current cleaning process, namely, lowering metal impurities of the wafer, lowering organic compound contaminants and reducing the number of micro-particles. Following the rapid development of sub-micron manufacturing technology, cleaning is increasingly critical with respect to micro-particles and metal impurities, and in particular with respect to the requirement for metal impurities.
In the current cleaning method for a wafer surface, the most common type of cleaning method is RCA cleaning technology. In this RCA cleaning technology, an weak acid or weak alkaline solution is used as a cleaning solution. The wafer is immersed in the cleaning solution having a pH value, and contaminants on the wafer surface are removed by appropriate stress. However, in the cleaning process of the back end metal manufacturing process of a semiconductor the metal atoms of a wire connection metal surface exposed by the wafer surface produces a chemical or an electrochemical reaction with acidic ion or alkali ions in the cleaning solution to form metal ions. Metal corrosion is formed on the wafer surface, which lowers product yield and increases production cost.
Accordingly, it is an object of the present invention to provide a cleaning method for a back end manufacturing of a semiconductor by employing cathodic protection to prevent metal corrosion on the wafer surface, and by means of a sacrificial anode to provide charges required by the metal layer of the wafer surface so that metal atoms on the wafer surface are not attacked by acidic ions or alkaline ions (for example Hxe2x88x92 and OHxe2x88x92). As a result of the present invention, the product yield is effectively improved and the production cost is reduced.
Another object of the present invention is to provide a cleaning method for a semiconductor manufacturing process to prevent metal corrosion. The method begins by providing a to-be-cleaned wafer having a metal layer thereon. The wafer is placed into a chemical cleaning equipment unit to clean the wafer surface with a chemical cleaning solution while the metal layer is protected with a cathodic protection. Then, the chemical cleaning solution is removed from the wafer by rinsing before drying the wafer.
Yet another object of the present invention is to provide a cleaning method employing a chemical cleaning solution to clean a wafer, whereby an externally applied current provides charges required for prevention of oxidation on the metal layer on the wafer surface so as to avoid metal corrosion on the wafer surface and to improve product yield and lower the production cost.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.